Flash Flood Warning 30, NWS Honolulu, HI

Area Forecast Discussion
National Weather Service Honolulu HI
353 AM HST Sat Apr 14 2018

.SYNOPSIS...
An upper level low west of the islands combined with enhanced
moisture spreading up from the southeast, will maintain the
threat of flooding into Sunday morning. The upper level low will
move away early next week, but lingering moisture over the islands
will keep the trades somewhat wet. Wind speeds will moderate
somewhat after the weekend with a weaker high passing north of the
area Tuesday.

&&

.DISCUSSION...
Heavy rains and thunderstorms will remain possible through tonight
as an upper low provides instability, and enhanced low level
moisture provides the fuel. A flash flood watch is in effect for
all islands as a threat of heavy showers and thunderstorms remains
for all islands through tonight. Last evening on Oahu, heavy
rains brought flash flooding to the eastern half of the island
with the highest rainfall totals of 5.31 and 4.94 inches and
Maunawili and Waimanalo, respectively.

Fresh trade winds will remain intact through the weekend, focusing
the heavy showers and thunderstorms over windward areas, but the
instability from the upper trough will allow these showers to
reach leeward areas of the smaller islands as well. On the Big
Island, windward areas will see similar weather with bouts of
heavy showers and isolated thunderstorms, while the leeward slopes
and coasts will see most clouds, showers, and possible
thunderstorms in the afternoon.

The low begins to move away Sunday, and weak ridging will rebuild
over the islands. This should hold through the middle of next
week. However, lingering moisture will continue to keep trades
somewhat wet, although with more subdued rain intensities. The
models disagree somewhat about how much moisture will be available
for trade wind showers, with the ECMWF trying a little harder to
advect drier air back over the islands. There are no strong
signals in the model trends right now, though.

A strong high will pass about 1200 miles due N of the islands
today, which will ramp the trades back up to windy levels over
the weekend. This high will continue eastward and weaken into next
week. A weaker high will pass farther N of the islands Monday
night and Tuesday, with trades at breezy to locally windy levels.
After that, the trades should moderate a bit as a subtropical
ridge is left behind N of the islands through the middle of next
week.

&&

.AVIATION...
Strong and gusty trade winds will persist through tonight.
Abundant moisture and unstable atmospheric conditions are
allowing heavy showers and isolated thunderstorms to develop
across much of the state early this morning. Expect widespread
and persistent MVFR conditions over most windward sections
through this evening. In addition, brief MVFR/IFR conditions are
possible near thunderstorms.

AIRMET Sierra remains in effect for mountain obscuration on
Kauai, Oahu, Molokai, Maui, and the windward Big Island. These
conditions may persist through this evening for most of these
islands. In addition, AIRMET Tango remains in effect for low-
level turbulence leeward of the higher terrain on all islands.
This AIRMET will likely remain in place most of this weekend,
since the low-level trade wind flow will be strong for the next
few days. Finally, we are mentioning the potential for icing in
the layered clouds above the freezing level.

&&

.MARINE...
With trade winds on the increase and an incoming large northwest
swell, a Small Craft Advisory (SCA) has been posted to cover all
waters through most of the weekend.

The new northwest swell is expected to peak this morning,
producing surf at the low-end warning level along north and west
facing shores through the day. Therefore, a High Surf Warning is
now in effect for most north and west facing shores through
tonight. The swell will subside through Monday. A small north
swell is expected mid-week with a moderate northwest swell
building Thursday night. As trade winds strengthen this weekend,
surf along east facing shores is expected to reach advisory level
as well, and an HSA will likely be issued. The elevated east-side
surf is expected to persist into the first half of next week. Surf
will remain small along south facing shores, but new swells from
the southern hemisphere will produce a modest increase starting as
early as Sunday.

Isolated thunderstorms are likely over coastal waters this morning.

See the Collaborative Surf Discussion for additional details on
surf and swell.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through late tonight for all Hawaii islands.

High Surf Warning until 6 AM HST Sunday for Niihau-Kauai
Windward-Kauai Leeward-Waianae Coast-Oahu North Shore-Oahu
Koolau-Olomana-Molokai-Maui Windward West-Maui Central Valley-
Windward Haleakala.

High Surf Advisory until 6 AM HST Sunday for Big Island North
and East.

Small Craft Advisory until 6 AM HST Monday for Maalaea Bay-
Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big
Island Southeast Waters.

Small Craft Advisory until 6 PM HST Sunday for Kauai Northwest
Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel-
Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui
County Windward Waters-Maui County Leeward Waters-Big Island
Windward Waters.

&&

Morrison/Ballard...Discussion
Houston...Aviation
Marine...Kinel

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HONOLULU HI
1049 PM HST FRI APR 13 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0842 PM     FLASH FLOOD      1 S NIU VALLEY          21.28N 157.74W
04/13/2018                   HONOLULU           HI   TRAINED SPOTTER

            TRAFFIC STALLED IN ALL LANES OF KALANIANAOLE HIGHWAY NEAR
            NIU VALLEY DUE TO 10-12 INCHES OF STANDING WATER ON
            ROADWAY. WATER IS STILL RISING.

0856 PM     FLASH FLOOD      AINA HAINA              21.29N 157.75W
04/13/2018                   HONOLULU           HI   COUNTY OFFICIAL

            KALANIANAOLE HIGHWAY CLOSED FROM AINA HAINA TO MAKAPUU
            DUE TO FLOODING.

0905 PM     TSTM WND DMG     KAIMUKI                 21.28N 157.81W
04/13/2018                   HONOLULU           HI   COUNTY OFFICIAL

            ROAD CLOSURE DUE TO DOWNED POWER LINES ON MAUNALOA AVE.
            BETWEEN 8TH AND 9TH AVE.

0935 PM     FLASH FLOOD      2 ESE MAUNAWILI         21.37N 157.74W
04/13/2018                   HONOLULU           HI   COUNTY OFFICIAL

            PARTIAL ROAD BLOCKED DUE TO MUD SLIDE AT KALANIANAOLE
            HIGHWAY AND KEOLU DRIVE.

&&

SHOUSTON

Special Weather Statement
National Weather Service Honolulu HI
213 AM HST SAT APR 14 2018

HIZ002>004-141315-
Kauai Windward-Kauai Leeward-Kauai Mountains-
213 AM HST SAT APR 14 2018

...A STRONG THUNDERSTORM WILL AFFECT KAUAI IN KAUAI COUNTY...

At 212 AM HST, a strong thunderstorm was located 6 miles southeast of
Poipu, or 11 miles south of Lihue, moving west at 20 mph.

Winds in excess of 30 mph are possible with this storm.

Locations impacted include...
Lihue, Kalaheo, Kekaha, Hanapepe, Omao, Koloa, Poipu, Lawai, Waimea,
Mana, Barking Sands, Kaumakani, Pakala Village, Eleele, Puhi and
Waimea Canyon State Park.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

LAT...LON 2195 15935 2188 15943 2188 15947 2189 15951
      2188 15953 2189 15956 2191 15960 2189 15961
      2196 15967 2199 15977 2206 15974
TIME...MOT...LOC 1212Z 106DEG 18KT 2182 15938

Morrison